1. Field of the Invention
This invention relates to the field of composite materials, especially energetic composite materials, composite articles, and methods for making and using the same. The composite materials of embodiments of the present invention are particularly useful as an energetic structural component, such as a reactive fragment, reactive projectile or casing of an explosive, pyrotechnic, gas generator and the like.
2. Description of the Related Art
Metallization of energetic materials is a method use to increase the total energy of an explosive whereby a combustible metal fuel is added to explosive formulations. Conventional metallized explosive formulations and other energetic materials commonly comprise a combination of metallic fuel particles, oxidizer particles, organic binder, and optionally energetic and non-energetic fillers. Aluminum is one of the most commonly used and well known metallic fuels, while ammonium perchlorate and/or ammonium nitrate are often selected as the oxidizer(s) of choice.
However, a drawback of conventional energetic materials is that the reaction between metallic particles such as aluminum and oxidizers such as ammonium perchlorate and ammonium nitrate is diffusion limited, inasmuch as the reactants must travel over a distance in the composition before reaching and reacting with one another As a result, conventional metallized energetic materials are more suitable for applications requiring relatively slow reaction events, such as in the case of underwater explosives. On the other hand, in applications requiring a relatively fast reaction event, such as in the case of metal driving and blast explosives, much of the metallic fuel may be wasted or not optimized in use due to the diffusion limiting reaction between the metallic fuel and oxidizer. Therefore, metallized energetic formulations generally are not used for these tasks.
Another drawback associated with conventional energetic materials is that the metallic particles, especially aluminum, tend to oxidize in stable non-inert atmospheres. In the case of micron-sized particles, oxidation at the aluminum surface may form an oxide layer, which increases the diffusion time required for reaction between the metallic particles and the oxidizer. In the case of nanometer scale particles (or nanoparticles), the oxide layer formed on the metallic particles may become sufficiently appreciable to constitute a weight penalty.
Additional drawbacks associated with conventional energetic materials involve agglomeration and migration of constituents, such as metallic particles or oxidizer particles, within an energetic article. Migration in particular can become a problem for cast energetic materials subjected to prolonged storage. Agglomeration and migration lead to inhomogeneity and increase the reactant diffusion distance, resulting in a slower burn rate and detrimentally affecting performance. As a result, some conventional energetics have limited shelf lives before they must be recycled or destroyed.
Still another drawback associated with energetic materials made from conventional compositions relates to their physical properties. Conventional energetic materials lack sufficient strength and rigidity to allow them to be used as structural components, such as weaponry cartridge cases. As a result, cartridge cases are traditionally made of metals. However, metallic cartridge cases are inert, relatively expensive, and carry a large weight penalty.
3. Objects of the Invention
It is one object of this invention to provide an energetic material that overcomes one or more, and preferably all of the above-discussed drawbacks associated with conventional energetic materials.
It is yet another object of this invention to provide methods for making the energetic materials and energetic articles of manufacture of the present invention.
It is another object of this invention to provide articles of manufacture, such as but not necessarily limited to ammunition casings and reactive projectiles, made from the energetic material of this invention.